Condensation derivative of rubber



Patentecl Apr. 15, 1941 CONDENSATION DERIVATIVE F RUBBER Thomas 0.Morris, Akron, Ohio, assignor to Wingfoot Corporation, Wilmington, Del.,a corporation of Delaware No Drawing.

Application April 1, 1937,

Serial No. 134,385

1 Claim.

This invention relates to the production of condensation derivatives ofrubber by treating rubber with boron fluoride. It includes the use ofboron fluoride complexes, such as ether and ester complexes, such as thecomplexes formed with dimethyl ether, methyl ethyl ether, di isopropylether, methyl acetate, ethyl formate, isopropyl acetate, etc. Itincludes the use of emulsifying and protective agents in the final stepof the process in which boron fluoride reacts on a rubber cement, thereacted cement is poured in water and emulsified and the solvent of thecement is volatilized from the emulsion, the condensation derivativebeing thereby precipitated. It also includes volatilization of thecement solvent from an alkaline emulsion.

Boron fluoride is a gas and it has therefore been found desirable toutilize this compound in the form of a complex. Ether and estercomplexes dissolved in benzene have given satisfactory results. Incarrying out the reaction the rubber cement is treated with the ethercomplex until a reaction product of desired properties is produced. Moreintensive action of the condensing agent on the rubber gives an endproduct of higher softening point than that obtained with less intensiveaction. Therefore the reaction with the boron fluoride is continued foronly a predetermined length of time in order to obtain the desired endpoint. The reacted cement is then poured into water. The water maycontain sodium sulfite as a reducing agent if desired or the sodiumsulfite may be omitted. It has been found that when the Water is madealkaline by any suitable reagent, such as soda ash, etc., on removal ofthe cement solvent by steam distillation the end product is obtained infinely divided form. The particles of the end product are however solarge that difliculty has been experienced in drying them. By adding anemulsifying and protective agent smaller particles are obtained. Sodiumstearate is quite satisfactory but foams to a considerable extent. Ithas been found that by precipitating the sodium stearate with a zinccompound such as zinc sulfate a precipitate of zinc stearate is formedaround the particles of the end product and serves as a protectivecolloid. By this procedure an end product of such fine particle size asto be readily dried is obtained and the foaming is not excessive. About1% of zinc stearate on the dry solids content of the bath is suitable.The resulting product is directly soluble in gasoline.

In carrying out the process the following general procedure may befollowed:

Pale crepe rubber is milled to a plasticity of about 300 (WilliamsPlastometer). This is dissolved in benzene to produce a 12.5% cement.This cement is brought to about boiling by heating with steam in thejacket. After cooling the jacket to about the boiling point of thebenzene the ether complex is added. 9.13 pounds of BF3(C2H5)2O dissolvedin an equal weight of benzene is added slowly to 1920 pounds of therubber cement. About 15 minutes should be consumed in adding the ethercomplex. The reaction vessel is equipped with a reflux condenser. Thereaction mixture is stirred during the addition of the reagent and thestirring is continued with sufiicient heat to cause the reaction toprogress until the desired reaction has taken place. A cement with aviscosity of about .28 to .30 minute (Gardner Mobilometer) will give aproduct suitable for coating compositions, etc. When the desiredreaction has been completed five pounds of water is added to the reactedcement to stop the reaction of the boron fluoride. The reacted cement isthen passed through a. filter into the precipitation Vessel.

The precipitation vessel contains about 4000 pounds of water warmed toF. 14.3 pounds of soda ash and 2.4 pounds of stearic acid are dissolvedin about 10 gallons of water. This is brought to a boil and the heatingcontinued until the acid is completely converted to soap. The soapsolution is then added to the water in the precipitation vessel. Whenthe soap solution is well dispersed the reacted cement is then turnedinto it with stirring and agitation. About 1.21 pounds of zinc sulfate(Zl'lSO4.7I-I2O) dissolved in one gallon of water is then added to theemulsion in the precipitating vessel. After the'stearate has beenconverted to the zinc salt the emulsion is subjected to steamdistillation to volatilize the benzene. As the benzene evaporates theend product is precipitated in finely divided form. This is filtered anddried, preferably in a vacuum.

Sodium sulfite may be added to the water of the precipitating bath andordinarily this will be desirable.

It may be desirable to treat the rubber cement with hydrochloric acidbefore adding the boron fluoride. The hydrogen chloride mayadvantageously be introduced in aqueous form. However when used inaqueous form it is important that the water be eliminated before addingthe boron fluoride complex. This may be done by boiling the cement undera reflux condenser with a trap in the reflux line to separate the water.

The process of treating rubber with a boron fluoride complex asdisclosed herein is claimed in my co-pending application Serial No.349,221 filed August 1, 1940.

I claim:

The method of producing a. condensation derivative of rubber whichcomprises treating rubher in solution with boron fluoride, pouring thereacted cement into water which contains sodium stearate, andemulsifying it therein, adding a zinc salt to convert the sodiumstearate to zinc stearate and then volatilizing the solvent of thecement to precipitate the condensation derivative of rubber.

THOMAS C. MORRIS.

